In many applications, especially low voltage drive applications, MOSFETs (metal-oxide-semiconductor field-effect transistors) with low Rdson (on-state resistance), low gate charge and a built-in body diode are used to achieve high efficiency. A body diode having low forward voltage (Vf) and low reverse recovery (Qrr) aids in reducing the overall loss, and may be critical in certain applications. As such, low diode forward voltage drop is typically one of if not the highest priorities among all device electrical parameters.
Bipolar operation of a body diode with a typical forward voltage of 0.8 to ˜1V is undesirable for reliable device operation and reduced conduction loss. A Schottky contact-based unipolar-type diode can be externally connected in parallel to a MOSFET as a separate chip (die) to accommodate current in the opposite direction. However, this approach increases package size and cost of implementation in power converters. This approach also introduces a high degree of parasitic inductance between separately-packaged devices, reducing efficiency and switching frequency. In the case of a diode integrated with a MOSFET, the parasitic inductance is reduced significantly. However, this approach conventionally utilizes the MOSFET conduction (active) area, therefore having a significant adverse impact on Rdson.
Thus, there is a need for a semiconductor device with low Rdson and having an integrated diode with low diode forward voltage and low reverse recovery.